1. Field of the Invention
The present invention relates generally to power generation systems and, more particularly, to systems incorporating gasification processes.
2. Background Art
Integrated Gasification Combined Cycle (IGCC) systems present an opportunity to deploy coal, an abundant resource, in an economical and clean manner, bringing improved efficiency and cost over conventional coal-burning steam turbine power generation systems as well as Natural Gas Combined Cycle (NGCC) systems. In an IGCC system, a carbonaceous fuel such as coal, or heavy oil, or petroleum coke is converted to a gaseous fuel, termed syngas, a mixture formed by partial oxidation at elevated temperatures. Components of syngas vary considerably depending on the fuel source and reaction conditions. For coal gasification with compressed oxygen, typical constituents of syngas include H2, CO, CO2, and CH4. In addition, syngas normally includes impurities such as sulfides, nitrogen components, and ash particles all of which are normally removed from the mixture prior to combustion in order to provide environmentally acceptable exhaust gases from the power system. Removal of these materials can introduce thermal inefficiencies to the overall gasification process.
IGCC and natural gas power generation systems commonly use air-fired combustors which produce exhaust containing a mixture of CO2, O2, H2O, N2 and nitrogen oxide products (e.g. NOx). The CO2 content in these gases is typically 3-5 percent by volume after combustion. To achieve a reduction of greenhouse gas emissions the CO2 can be recovered from the combustion exhaust with various physical and chemical solvents. However, cost of such CO2 capture is on the order of $150 per ton of carbon and this can increase the cost of electricity by 2.5 cents to 4 cents per kWh. Processes that can be used to extract CO2 from the exhaust gases may also scrub NOx. However, additional steps for NOx removal may be necessary to meet regulatory standards It would therefore be advantageous to provide high efficiency power generation fuel processes which produce lower levels of greenhouse gases and contaminants which are costly to remove.